Conventionally, image analysis on medical image data involves quantitative evaluation of a space (also called “joint space”) between bones that form a joint therebetween. For example, the distance between two points designated by an operator in two-dimensional projected image data captured by plain radiography is measured as the width of a joint space. Also for example, the area of a region designated by an operator in projected image data is measured as the size of a joint space.
Various techniques have been proposed for enabling automatic measurement of a joint space. For example, based on information on anatomical features of a joint to be evaluated, a region corresponding to the joint is extracted from projected image data. Thereafter, the maximum and minimum values of the width of a joint space and the area of a corresponding region are automatically measured. For such a technique, dedicated computer programs for different kinds of joint, such as one for knee joints and one for hip joints, are developed.